The invention relates to vascular repair devices, and in particular intravascular stents, which are adapted to be implanted into a patient's body lumen, such as a blood vessel or coronary artery, to maintain the patency thereof. Stents are particularly useful in the treatment of atherosclerotic stenosis in arteries and blood vessels.
Stents are generally tubular shaped devices which function to hold open a segment of the blood vessel or other body lumens such as a coronary artery. They also are suitable for use to support and hold back a dissected arterial lining that can occlude the fluid passageway. At present, there are numerous commercial stents being marketed throughout the world. For example, the prior art stents depicted in FIGS. 1-4 have multiple cylindrical rings connected by one or more undulating links.
FIG. 1 depicts a prior art stent 10 mounted on a conventional catheter assembly 12 which is used to deliver the stent and implant it in a body lumen, such as a coronary artery, peripheral artery, or other vessel or lumen within the body. The catheter assembly includes a catheter shaft 13 which has a proximal end 14 and a distal end 16. The catheter assembly is configured to advance through the patient's vascular system by advancing over a guidewire by any of the well known methods of an over-the-wire system (not shown) or a well known rapid exchange catheter system, such as the one shown in FIG. 1.
Catheter assembly 12 as depicted in FIG. 1 is of the well known rapid exchange type which includes an RX port 20 where the guidewire 18 will execute the catheter. The distal end of the guidewire 18 exits the catheter distal end 16 so that the catheter advances along the guidewire on a section of the catheter between the RX port 20 and the catheter distal 16. As is known in the art, the guidewire lumen which receives the guidewire is sized for receiving various diameter guidewires to suit a particular application. The stent is mounted on the expandable member 22 (balloon) and is crimped tightly thereon so that the stent and expandable member present a low profile diameter for delivery through the arteries.
As shown in FIG. 1, a partial cross-section of an artery 24 is shown with a small amount of plaque that has been previously treated by an angioplasty or other repair procedure. Stent 10 is used to repair a diseased or damaged arterial wall which may include the plaque 26 as shown in FIG. 1, or a dissection, or a flap which are sometimes found in the coronary arteries, peripheral arteries and other vessels.
In a typical procedure to implant prior art stent 10, the guidewire 18 is advanced through the patient's vascular system by well known methods so that the distal end of the guidewire is advanced past the plaque or diseased area 26. Prior to implanting the stent, the cardiologist may wish to perform an angioplasty procedure or other procedure (i.e., atherectomy) in order to open the vessel and remodel the diseased area. Thereafter, the stent delivery catheter assembly 12 is advanced over the guidewire so that the stent is positioned in the target area. The expandable member or balloon 22 is inflated by well known means so that it expands radially outwardly and in turn expands the stent radially outwardly until the stent is apposed to the vessel wall. The expandable member is then deflated and the catheter withdrawn from the patient's vascular system.
The guidewire typically is left in the lumen for post-dilation procedures, if any, and subsequently is withdrawn from the patient vascular system. As depicted in FIGS. 2 and 3, the balloon is fully inflated with the prior art stent expanded and pressed against the vessel wall and, in FIG. 3, the implanted stent remains in the vessel after the balloon has been deflated and the catheter assembly and guidewire have been withdrawn from the patient.
FIG. 4 illustrates the prior art stent 10 in some detail. The undulating portion 27 of the links 28 are positioned between two struts 29A/29B. The links 28 all have the same undulating pattern on the strut. Consequently, the bending stiffness profile of the stent is substantially constant along the length of the stent.
Typically, stent design has focused on maximizing the flexibility of the stent. However, less attention has been paid to the sharp change in flexibility of the stent delivery system at the beginning and ending points of the stent. FIG. 5 illustrates a stiffness profile of a typical traditional stent delivery system. As FIG. 5 illustrates, the stiffness of the system sharply increases at the one end of the stent, with very little transition in stiffness between the stent and the portion of the stent delivery system immediately adjacent the stent. What is desired is a stent delivery system having a stent that smoothes the stiffness transition in the stent delivery system at the ends of the stent itself.